Identifying Channel Morphology Changes in Response to the Removal of the Glines Canyon Dam on the Elwha River, WA

The ongoing removal of the Glines Canyon and Elwha Dams on the Elwha River, Washington, is the largest dam-removal project in history. Our research quantified sediment deposition, erosion and channel changes to the Elwha River following the removal of the Glines Canyon Dam. Documenting river channel response to this exceptional sediment pulse could improve models of the impacts of future dam removals on similar gravel-bed rivers. We measured changes in channel morphology and sediment-size distribution at four field sites located 2 to 6 km downstream of Glines Canyon Dam. In the first two months following the initial sediment release in October 2012, the mean sediment size on the surface of the channel bars abruptly decreased from approximately 18 cm to sites, as well as the longitudinal growth of several bars throughout the study area. The gravel bars at three study sites have increased in volume by ≥5 percent during the dam removal process. By spring 2013, channel features that were present before the dam removal began to re-emerge due to reduced sediment flux through the system. We anticipate that the gravel bar formations in this reach will continue to evolve as the dam removal continues to add new sediment and as seasonal discharges remobilize the existing sediment